Feast or Famine?—The rewards and risks of fasted cardio workouts

October 2014 View more

iStock_000003176409Large_800pxIt’s been debated for years: should you eat before working out in the morning, or will you lose more weight faster if you exercise on an empty stomach? It all depends on the type of training you’re into and for what reason.


Some experts say if you exercise on an empty stomach, it can speed up fat- burning and weight loss. The idea is that all the necessary energy you need during the workout comes from stored fat. “The reasoning behind this is that your body is already low on circulating blood glucose prior to the workout. Thus, you run through your glycogen stores sooner and start to metabolize fatty acids sooner, burning more fats,” said Dr. Michael Hartmann, Naperville Marathon race director for Edward Hospital. However, Dr. Hartmann cautions that fasted cardio workouts only benefit certain people. “Endurance athletes looking to increase their efficiency of fat metabolism may benefit from fasted cardio workouts. Having an increased ability to derive energy from fat metabolism benefits marathoners, ironmen, and endurance athletes by training their bodies to run while glucose and/or glycogen deficient,” said Dr. Hartmann.


However, for most people, proper fueling before training is very important to their overall health and effectiveness of the workout. Otherwise, experts say you may not have the energy to keep your workout up to par. You might feel like you’re dragging through the routine. Since glucose is the main method of fueling the body in exercise, experts also say it’s a good idea to have it circulating in your bloodstream so the body can use it as energy.


Dr. Hartmann says certain people must fuel before their fitness. “I do not believe fasting cardio should be performed in certain types of populations. First, diabetics should not perform fasting cardio exercise. The obvious fluctuations in their daily blood sugars, along with medications such as insulin or oral agents, make fasting cardio very dangerous for these people. People just starting an exercise regimen should not perform fasted cardio workouts either. Starting a workout without eating can cause the person to develop weakness, lightheadedness, or dizziness resulting in early termination of the workout. Stopping the workout early because of not fueling properly before the workout defeats the purpose of the workout,” said Dr. Hartmann. A workout should make you feel strong and energized, not drained and defeated. “Make it fun and take the time to go full-throttle! If our body gets used to just going through the motions during your workout, we are not achieving anything. We may as well be sitting on the couch.”

Experts say if you have the energy to start strong, chances are that your workout will be much more efficient and enjoyable, and it won’t feel like a dreaded chore. “Ultimately, I believe the risks of fasted cardio training and exercise outweigh the benefits,” said Dr. Hartmann.


Recommended foods to help you power-up before your workout.

  • Light snack 30-45 minutes prior to each workout. Think fruit, oatmeal, whole grain cereal or a protein bar.
  • Any workout lasting longer than one hour needs refueling with glucose supplementation. Try energy gels.
  • For post workout refueling, go for carbohydrates to protein in a 3:1 ratio. Dr. Hartmann recommends a glass of chocolate milk.
Courtesy: Dr. Michael Hartmann, Race Medical Director for the Edward Hospital Naperville Marathon